//=============================================================================
// LazyParser.NET - C# Expression Parser for .NET 2.0 
//
// Copyright (c) 2008 Philippe Leybaert
//
// Permission is hereby granted, free of charge, to any person obtaining a copy 
// of this software and associated documentation files (the "Software"), to deal 
// in the Software without restriction, including without limitation the rights 
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 
// copies of the Software, and to permit persons to whom the Software is 
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in 
// all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
// IN THE SOFTWARE.
//=============================================================================

using System;

namespace Activa.LazyParser
{
    public class CoalesceExpression : Expression
    {
        private readonly Expression _value;
        private readonly Expression _valueIfNull;

        public CoalesceExpression(Expression value, Expression valueIfNull)
        {
            _value = value;
            _valueIfNull = valueIfNull;
        }

        public override ValueExpression Evaluate(IParserContext context)
        {
            ValueExpression result = _value.Evaluate(context);

            if (result.Value == null)
                return _valueIfNull.Evaluate(context);

            return result;
        }

        public override string ToString()
        {
            return "(" + _value + " ?? " + _valueIfNull + ")";
        }
    }
}